That's the point: Truecrypt wasn't open source, at least not in the FOSS sense. I'm not a lawyer, but my understanding is that there is a ton of ambiguity over whether you can make modifications to the Truecrypt source code and still abide by the license. The source code was only open in that no one really trusts any crypto that can't be reviewed, so the source code was released to aid that.
That's the point: Truecrypt wasn't open source, at least not in the FOSS sense. I'm not a lawyer, but my understanding is that there is a ton of ambiguity over whether you can make modifications to the Truecrypt source code and still abide by the license. The source code was only open in that no one really trusts any crypto that can't be reviewed, so the source code was released to aid that.